In recent years, a higher recording density of a storage medium such as a magnetic disk has been promoted in the field of a disk storage apparatus such as a hard disk drive (hereinafter, referred to simply as a disk drive). In the disk drive, a large number of cylinders (tracks) are arranged in a radial direction on the disk, the cylinder comprising a servo area (hereinafter, referred to as a servo sector) in which servo information is recorded. The servo information is used to detect a position of a head over the disk, and includes a preamble in which address data including a cylinder number and a servo sector number is recorded and a burst.
In the magnetic disk apparatus, a magnetic head is positioned on a target track on the basis of read servo information. However, as storage media come to have higher densities, the proportion of noise components in a servo signal tends to be relatively increased because of floating fluctuations, etc of the magnetic head. In control of off-track detection of a magnetic disk apparatus, these noise components cause a demodulation error of a position error signal (PES) to be demodulated. Also, due to a demodulation error of a position error signal (PES), it may be often occurred that the off-tracking of the head cannot be correctly detected. As a result, the risk of adjacent data being deleted when user data is written has been increasing.